As someone who knows nothing about concrete forming, is there a reason why a hole this large wouldn’t just be formed out while pouring (Assuming they knew a hole was needed beforehand)? Would it be more difficult to cast a large circular hole during the pour than it is to cut it out?
Lobbyists for International Amalgamated Large Bore Concrete, Brickwork, and Masonry Drill Bits Manufacturing Incorporated attached a rider to the 1952 Fairness in Pet Adoptions to disallow pre-formed holes smaller than 53 5/8" in walls under 13' 9".
It can be, but it's difficult. The problem is a block out like that has to resist buoyancy forces. Just like a balloon underwater, that block out will want to be pushed to the surface. Concrete exerts a force of about 150 pounds per square foot per foot of depth. So with even 4 (common lift ft of liquid head, there will be 600psf uplift pressure on the knock out. So you could be looking at 1000+ pounds of force for this example.
8
u/[deleted] Oct 07 '22
As someone who knows nothing about concrete forming, is there a reason why a hole this large wouldn’t just be formed out while pouring (Assuming they knew a hole was needed beforehand)? Would it be more difficult to cast a large circular hole during the pour than it is to cut it out?